1. Field of the Invention
This invention relates to stabilized silica-base defoamer compositions and their use in aqueous systems.
2. Description of the Prior Art
Silica-base defoamers are well known as defoamers for aqueous systems. One of the problems of such defoamers, however, is the tendency for the silica particles to settle out of the carrier liquid (usually a hydrocarbon or natural oil) in which they are suspended. Only the use of extremely fine particle silica achieves some degree of stability. However, fine particle silica is of limited supply and is more expensive than other grades.
Quick-chilled amides are also well known as defoamers for aqueous systems. In addition, it is known to use mixtures of silica and quick-chilled amides, where each is present in defoaming quantities.
The following patents disclose the defoaming properties of various components of the subject compositions, but none teach their combination for the purpose of increasing the stability of silica-based defoamers.
U.S. Pat. No. 3,076,768 (Boylan) discloses silica-base defoamers containing hydrophobic silica, hydrocarbon oil, and a spreading agent.
U.S. Pat. No. 3,207,698 (Liebling and Canaris) discloses silica-base defoamers containing hydrophobic silica of a particular nature and hydrocarbon oil.
U.S. Pat. No. 3,652,453 (MacDonnell) discloses amide-base defoamers containing quick-chilled amides, hydrocarbon oil, and oil-soluble organic polymers.
U.S. Pat. No. 3,677,963 (Lichtman and Rosengart) discloses amide-base defoamers containing quick-chilled amides, hydrocarbon oil, oil-soluble organic polymers and fats.